To improve network reliability against failures, the following methods have conventionally been applied in an ATM network, where a protection channel is provided in addition to a working channel.                (1) Automatic protection switching (APS) of the physical layer (hereafter referred to as the ‘physical layer APS’) which is defined in SDH, SONET and the like, or        (2) Path re-establishment and switchover using signaling procedure.        
The above methods, however, have disadvantages shown below:
In the method (1), a bandwidth for a protection channel must constantly be reserved corresponding to bandwidth of a physical channel. This reduces efficient use of network resources. In the above method (2), long interruption time against normal service is needed because of substantial time consumption for exchanging signals between nodes, and for executing a software process sequence to search for an idle route and to carry out path establishment and switchover.